1. Field of the Invention
The present invention relates to a float valve device in which a float rises within a housing when a liquid level rises and in which an opening communicating with an exterior is closed when the liquid level has attained a predetermined height, and more particularly, to a valve device suitable as a float valve device which allows fuel vapor in a fuel tank of an automobile to escape to a canister, which, when a fuel liquid level exceeds a predetermined value, closes an opening so as to prevent fuel from flowing to an outside, and which performs a full-tank regulation at the time of fuel supply.
2. Description of the Related Art
For example, inside the fuel tank of an automobile, there is arranged a float valve device which allows fuel vapor to escape to a canister arranged outside to thereby prevent an increase in tank inner pressure, which closes an opening communicating with the canister when the fuel liquid level exceeds a predetermined height, to thereby prevent fuel from flowing to an outside, and which performs a full-tank regulation at the time of fuel supply.
As an example of the float valve device described above, Japanese Patent Application Laid-open No. Hei 07-279789 discloses a liquid level control valve including: a seat portion (corresponding to valve seat) including a first flat surface portion arranged at an opening of a fuel tank communicating with one end of a passage which communicates with a canister at the other end thereof; a valve member including a first flat surface portion held in contact with the flat surface portion of the seat portion; and a float floating within the fuel tank due to a buoyancy of the fuel and adapted to make the seat portion abut the valve member so as to close the opening by upwardly pressing the valve member with a top portion thereof in response to a rise in the fuel liquid level. Further, the valve member is engaged with the float so as to be capable of relative movement, and the top portion of the float is formed by a protrusion including a three-dimensional curved surface formed at a center of an upper portion of the float.
When the float rises due to the rise in the fuel liquid level, the top portion of the float presses the valve member upwardly and brings the valve member into contact with the seat portion to thereby close the opening. Because the valve member is capable of relative movement with respect to the float, if, at some circumstances, an attitude of the float is inclined with respect to the opening due to inclination of a vehicle or the like, the attitude of the valve member is corrected as appropriate, and the valve member is firmly held in contact with the seat portion over an entire periphery of the seat portion, thereby closing the opening.
In the float valve device constructed as disclosed in Japanese Patent Application Laid-open No. Hei 07-279789, when the fuel liquid level once risen is lowered, the buoyancy applied to the float is reduced, and hence the float descends due to its own weight to return to an original position, and the opening is opened again.
However, in a state in which the opening is closed with high air tightness by the valve member arranged on the upper portion of the float, the inner pressure of the fuel tank is applied as a force for pushing up the valve member, and hence even when the fuel liquid level is lowered and the buoyancy applied to the float is reduced to thereby attain a state in which the opening ought to be opened due to the weight of the float itself, the valve member may sometimes remain attached to the opening, keeping the opening closed. If opening of the valve upon lowering of the fuel liquid level is not thus effected with satisfactory responsiveness, there is a risk of a vapor pressure within the fuel tank being excessively increased, even temporarily, which is not desirable.